1. Field of the Invention
This invention relates to a supervisory image communication system through an ISDN (Integrated Service Digital Network) wherein a parent station and a plurality of child stations are interconnected by way of an ISDN switched network such that any of the child stations transmits call originating information to originate a call to the parent station whereas the parent station supervises, in response to the call originating information from the child station, the state of the child station in accordance with image information inputted thereto from the child station.
2. Description of the Related Art
Conventional supervisory image communication systems of the type mentioned normally have such a form that, when, for example, a burglar sensor or a like emergency sensor provided at a child station is turned on, the child station first originates a call to a parent station which is a center station, and after the parent station responds to the originating call, the child station transmits emergency information corresponding to the turning on of the sensor to the parent station. Thus, the parent station receives the emergency information and inputs, in response to the thus received emergency information, image information thereafter transmitted thereto from the child station to supervise the state of the child station. In other words, the parent station gets a reason of origination of a call from a child station, that is, a type of a call such as an emergency call arising from turning on of such a burglar sensor as described above or from scanning of switches, status information of the child station and other necessary station after it is connected to the child station by way of a circuit.
With the conventional systems, since the parent station gets, when a call originating reason occurs with a child station, the call originating reason after it responds to the originating call from the child station in this manner, connection of a circuit must be performed even in response to an originating call which is originated by another reason unnecessary for supervision. This results in a disadvantage in that it requires a corresponding communication cost. Further, there is another disadvantage in that, for example, when an originating call from a second child station arrives at the parent station during communication of the parent station with a first child station, in order for the parent station to get a call originating reason of the second child station, complicated operations are required that the parent station stops the communication with the first child station and responds to the originating call from the second child station.